I remember the builder of our home mentioned that only a furnace filter is required and having both furnace and return air grill filter would slow the air down too much.
I just called my friend, an HVAC tech on the job right now, and he says only one is required at the return air. He doesn't understand why they would want to put a grill filter in if there is already one at the return air. They only reason he could understand
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We've all heard noisy returns. How do you quiet them down? Make the return air duct longer...adding length slows air velocity. Or... increase ...
To answer this question you have to consider if air duct cleaning, electrostatic filter, or an HEPA air filter will accomplish what you are trying to achieve which is air purification. Should we worry about cleaning our air ducts is a question that can’t be answered with a simple YES or NO answer. In this article we’ll examine several possibilities that might solve the dirty air problem.
Stachybotrys Chartarum Mold and other molds:
There is one very serious reason that qualifies for a definite YES. If you
observe that there is substantial visible mold growth inside hard surface sheet metal ducts or on other components of your heating and cooling system. Several important points to understand concerning mold detection is many sections of your heating and cooling system may not be accessible for a visible inspection. You should be aware that although a substance may look like mold, a positive determination of whether it is mold or not can be made only by an expert and may require laboratory analysis for final confirmation. If you suspect you have mold contact a microbiology laboratories to inspect your system to determine the extent and danger you may encounter. If the insulated covering your air ducts gets wet and moldy it should be cleaned and if this is not possible it should be removed and replaced. If the conditions causing the mold growth in the first place are not corrected, the mold growth will continue to worsen. The CDC (Centers for Disease Control) states it is prudent practice and recommends that they be removed.
Air pollutants commonly found in your home environment:
Once you get past mold that can cause serious illness or even be life threatening, you should consider indoor air pollutants such as dust, smoke, pollen, animal dander, tobacco smoke, particles generated from combustion appliances such as cooking stoves, and particles associated with tiny organisms such as dust mites, molds, bacteria, and viruses. They also come from building materials, furnishings, and the use of products such as adhesives, paints, varnishes, cleaning products, and pesticides.
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